1. Field of Invention
The present invention relates to a hydrocarbon-sensing apparatus and, more particularly, to a conductive polymer-based hydrocarbon-sensing apparatus including multiple sensing sections for contacting a layer hydrocarbon.
2. Description of Related Art
Pollution of reservoirs, rivers, or groundwater has new become a global problem. Such pollution may be caused by illegally dumping waste into water source. Moreover, oil may leak from tanks or pipes broken in an earthquake, for example. Thus, severe contamination of environment occurs.
Hydrocarbon-based fluid such as gasoline or diesel has a specific gravity smaller than that of water. Therefore, hydrocarbon-based fluid tends to float on water. When tanks that contain hydrocarbon-based fluid are located on the ground for some time, the hydrocarbon-based fluid is very likely to leak from the tanks. Hydrocarbon-based fluid that leaks from a tank may penetrate the ground so as to float on groundwater. Various devices have been devised for detecting contamination of groundwater caused by hydrocarbon fluid. Such devices can be found in U.S. Pat. Nos. 4,131,773, 4,223,552, 4,434,650, 4,563,674, 5,264,368, 5,444,383 and 5,514,338.
FIG. 1 shows a conventional hydrocarbon leak sensor incorporating a probe P. A portion of probe P is immersed in a well to be monitored and an upper end of probe P is fixed onto the wall of the well. Probe P incorporates a petroleum sensor made of conductive polymer in the form of a cable, for example, AMC-5016 (1932TC) made and sold by a Canada-based company, Armstrong Monitoring Corporation. The resistivity of such petroleum sensor is about several Kxcexa9/m in the air or water and rises dramatically to about 20Mxcexa9/m when such petroleum sensor contacts hydrocarbon or petroleum. Rise in resistivity of such petroleum sensor can be taken as presence of hydrocarbon or petroleum. The resistance (the unit is xcexa9) of probe P rises at a lower rate and to a smaller extent as a shorter section of probe P contacts hydrocarbon. In practice, probe P can be used to detect presence of a layer of hydrocarbon as thin as 0.8 mm. The rise of the resistance of probe P is too small to recognize when probe P contacts a layer of hydrocarbon thinner than 0.8 mm. Therefore, probe P cannot sense hydrocarbon leak or spill at an early stage. Furthermore, when leaking or spilling at a low flow rate, due to vaporization, hydrocarbon may not form a layer thick enough for probe P to sense. In other words, it is unlikely to be able to detect a leak or spill before significant damage has occurred. Moreover, a hydrocarbon layer on groundwater cannot be sensed when the groundwater surface rises above the upper end of probe P or when the groundwater surface descends below a lower end of probe P. To overcome this drawback, a lengthened probe is required. However, this increases cost and limits its applications.
Thus, it is desirable to provide an improved hydrocarbon sensor in order to overcome the above-mentioned drawbacks encountered in prior art.
It is an objective of the present invention to provide an apparatus for monitoring presence of hydrocarbon-based fluid wherein a sensing cable is provided in a wave-like arrangement. Thus, the sensing cable includes a number of sensing sections for contacting a layer of hydrocarbon-based fluid on the water surface. When contacting a layer of hydrocarbon-based fluid, the sensing sections generate a corresponding number of signals that add up to increase the signal intensity. A layer of hydrocarbon-based fluid can thus be sensed by means of the sensing cable even it is very thin. That is, the present invention can warn of hydrocarbon leak at an early stage or at a low flow rate so that an appropriate action can be taken before significant damage is made.
It is another objective of the present invention to provide an apparatus for monitoring presence of hydrocarbon-based fluid wherein a sensing cable is provided on a buoy for floating on the water surface. Thus, it is assured that the sensing cable always contact a layer of hydrocarbon-based fluid on the water surface no matter how the water surface changes.
To accomplish the above objects and features, the apparatus of the present invention comprises a buoy for floating on the water surface and a sensing cable made of conductive polymer. The sensing cable is mounted on a periphery of the buoy in a wavelike shape, thus forming a plurality of sensing sections for contacting a layer of hydrocarbon-based fluid on the water surface. When contacting a layer of hydrocarbon-based fluid, a signal is generated in. each of the sensing sections, and the signals add up before transmitting to the monitoring and warning unit through the signal line. By utilizing this, a sensitivity of a hydrocarbon-sensing apparatus is significantly increased according to the present invention.
The above and other objects, features and advantages of the present invention will become apparent from the following description taken with the attached drawings.